you can make a reg file,which contains "HKEY_LOCAL_MACHINE\SYSTEM\RAdmin\v2.0\Server\Parameters\DisableTrayIcon" and its value is set to "01 00 00 00" , or simply out one on a machine which has already hide tray icon, then you can use "regedit /s aa.reg".
Try it.

Special build of Radmin 3.0 that allows to hide the tray icon of Radmin server is released. This build is available to every registered user on request. Please send your requests for the special build to sales@famatech.com